[TenTec] "Tuning" antennas; baluns

At 10:30 AM 9/23/97 CDT, you wrote:
>Now I'm getting confused..... Doesn't an antenna act and resonate
>differently depending on it's height (I think). Is this true? I've tuned
>antenna's 10 feet of the ground, and had to retune when they were 60 feet off
>the ground.
Your correct. Reflections from the ground will change the resonant frequency of
the antenna wires, be it a dipole type antenna or a loop type antenna. LESSON:
Always try to raise your antenna to the height that your going to use it, and
then cut it to the resonant frequency that you want. If you can't reach the
antenna, when it's at the height that you are going to operate it, you can cut
the transmission line (either coax or open wire line) to a half wave length (or
multiple half wave lengths), connect the transmission line to the antenna, and
measure the resonant frequency of the antenna, down at the input to the
transmission line. The reason you can do this is because the impedance seen at
one end of a half wave length line exactly repeats at the other end.
>
>Also, I thought a tuner would correct the L and C to obtain resonance (within
>reason) so you could resonate any object... screen door, gutters, long wire,
>etc. Ok, I probably need to read more.
I think everyone can find something that can WORK FOR THEM. However, as Stuart
explains, a tuner is not resonating the screen door, gutter, long wire, etc.,
it is transforming the 'real' and 'imiginary' impedance presented at the INPUT
of your transmission line, to something that your rig will tolerate. Hopefully
a resistive 50 ohms with no capacitative or inductive reactance. A 'tuner' will
do nothing to or for the screen door, etc.
>
>Rick (N9THC)
>- - - - - - - - - - - - - - Original Message - - - - - - - - - - - - - -
>Hello all,
>
>Now, to try to summarize a complex subject:
>
>The concept of resonance, and tuning to resonance for an ANTENNA, must
>involve
>changing its Physical Dimensions. Once you have cut it to some size, it will
>have certain resonant properties. No amount of "tuning" of L and C circuits
>at the shack end of the transmission line will alter the resonant dimension
>of the antenna up in the air. Tuning is defined as affecting resonance; and
>the
>antenna resonance depends on its dimensions in terms of wavelengths or
>fractions thereof.
YES..YES...YES...YES
>
>The only thing you are "tuning" in the Antenna Matching device is actually
>"adjusting" the values of the L and C of those tuned circuits. However, you
>are MATCHING the transmission line to the rig,
YES..YES..YES..YES
>
>In fact, I hope all will agree or will measure, that even with an antenna
>matching device, (which for years was mistakenly called a "tuner"), you still
>have standing waves on the transmission line, and the matching device is just
>there to TRANSFORM a complex impedance at the shack end of the line to a
>value that more closely matches your transmitter.
YES..YES..YES..YES
>
>I hope this helps divide the concepts into their proper areas. Antennas
>resonate depending upon their physical structure and dimensions.
>
>73, Stuart K5KVH
>
I urge everyone who does not have a full understanding of antennas and
transmission lines and tuners (or matching devices) to SAVE Stuarts notes. In
the most clear terms possible, Stuart has explained the differences between the
three and what you CAN do and what you CAN NOT do with a tuner.
Chester Alderman
<color><param>0000,0000,ffff</param>W4BQF -- Tom
</color><color><param>ffff,0000,0000</param>chestert@pressroom.com
</color>
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